Decoding of Ambisonics representations for a stereo loudspeaker or headphone setup is known for first-order Ambisonics, e.g. from equation (10) in J. S. Bamford, J. Venderkooy, “Ambisonic sound for us”, Audio Engineering Society Preprints, Convention paper 4138 presented at the 99th Convention, October 1995, New York, and from XiphWiki-Ambisonics http://wiki.xiph.org/index.php/Ambisonics#Default_channel_conversions_from_B-Format. These approaches are based on Blumlein stereo as disclosed in GB patent 394325.
Another approach uses mode-matching: M. A. Poletti, “Three-Dimensional Surround Sound Systems Based on Spherical Harmonics”, J. Audio Eng. Soc., vol. 53(11), pp. 1004-1025, November 2005.